This type of the clamping device has been disclosed by Japanese Utility Model Publication No. 6-23822, Japanese Laid-open Patent Application No. 61-244906 and Japanese Patent Publication No. 7-26711 (referred to as “first document”, “second document” and “third document” in turn hereinafter).
In the first document, a portion in which slantwise grooves are defined to make a worm screw mesh with the grooves, is swollen in the diametrical direction to distance from a hose-forming section so as to prevent an incidental damage on the hose. This prevents a maximum surface pressure from exerting at the contact portion between a band and the hose, so as for the band not to stick into the slantwise grooves due to the action of the screw worm.
In the second document, it is taken into consideration that an increased width of gear grooves tends to tear an outer band upon tightening the band when the gear grooves are formed by means of a punching procedure. Instead of the punching procedure, a drawing and extrusion method (half-cut procedure) are used as an example of forging procedure to form the gear grooves. This enlarges a contact area in which a worm screw gets meshed with the gear grooves so as not to easily tear the band when tightened with an increased torque.
In the third document, the document discloses a bias structure as an elastic accumulation device which gives an urging force to a strap by means of multiple types of spring. With the use of these springs, the structure makes up for a tightening force by an amount reduced after the strap is tightened so as to minimize the reduced amount of the tightening force of the strap.
In the structure where the slantwise grooves are swollen as disclosed in the first document, the structure increases a bending rigidity of the band in its circumferential direction. Under the above structure, it becomes necessary to apply a larger amount of tightening force to the band so as to increase a sliding pressure of the worm screw against the slantwise grooves, thus producing a possibility to do damage on the screw worm and the slantwise grooves so as to lose the normal function of the band.
A housing in the first document seems to be secured to the band by bending a lower end portion of the housing in the manner depicted by Figures attached to the first document. For this reason, the housing is subjected to a reactionary force via the worm screw from the band upon tightening the worm screw, thus deforming the lower end portion of the housing to extend in the diametrical direction. This decreases a meshing allowance of the worm screw against the slantwise grooves, thus increasing the sliding pressure between the worm screw against the slantwise grooves so as to aggravate the above inconvenience.
A meshing allowance of the worm gear against the gear grooves in the second document is due to the valley portions of the worm gear and the linear convex portions of the outer band. The structure permits the outer band to compensate the bending rigidity by an amount which would be lost when the grooves are perforated through, while at the same time, increasing the reactionary force, to which the worm gear is subjected through the band.
For this reason, a large amount of the reactionary force increases the sliding pressure of the worm gear against the gear grooves to do damage on the gear grooves or excessively wear the valley portion of the worm gear so as to bring it out of mesh especially when tightly winding the band.
The third document shows that a strap is tightened against a rubber hose by the force of approx. 10-30 kg/cm2 with the compressibility of the rubber hose as approx. 20-30%. This is effective in compensating the tightening force of the band by an amount in which the rubber hose contracts although it raises a manufacturing cost due to an increased number of component parts with a complicated structure.
Judging from the manner as depicted in FIGS. 3 and 10 of the third document, the teeth portion is seemed to be formed by means of an impression procedure. For this reason, a meshing allowance of a screw bolt against the teeth portion is due to the valley portions of the screw bolt and the teeth portion as described in the second document. This increases the sliding pressure of the screw bolt against the teeth portion to do damage on the teeth portion and the screw bolt.
Judging from the housing partly notched in the second document, the lower end portion of the housing is seemingly bent against an inner side of the strap. This produces a deforming force on the housing to disengage the screw bolt out of the teeth portion due to the larger amount of the reactionary force, to which the housing is subjected through the strap when tightly winding the strap around the connecting portion.
In any of the documents mentioned above, it is not sufficient to cope with the above inconveniences especially when tightening the strap with the increased torque.
Therefore, it is an object of the invention to overcome the above drawbacks, and provide a clamping device for connection which is capable of increasing a contact area between a worm screw and an array of teeth portion, while decreasing a sliding pressure per a unit area therebetween, thus maintaining a good meshing condition between the worm screw and the array of teeth portion for an extended period of time when tightening a strap band with an increased torque.